1. Field of the Invention
The present invention relates to a slide table in which a voice coil motor is employed and, more particularly, to a slide table which is suitably incorporated into an ultrasonic microscope for high speed scanning of a probe, sample, or the like.
2. Statement of the Related Art
Conventionally, an apparatus such as an ultrasonic microscope which requires the scanning of a sample with high precision incorporates therein a precision slide table with air bearings, such as disclosed on page 750 of "Precision Machine" 51-4 (1985). In this slide table, a sample (or acoustic lens) is placed on a same base supported by the air bearings, a voice coil motor drives the slide table to move it reciprocatingly, and this reciprocating movement is transmitted to the sample table. In the above structure of the slide table, a bobbin having a coil of the voice coil motor wound therearound is secured to a carriage by which a drive shaft is supported. The carriage is reciprocatingly moved while it is being guided on and along its supporting plate by ball bearings. The axial movement caused by the voice coil motor is transmitted to the sample table via a steel ball provided at a tip end of the drive shaft and via a magnet piece attached to an end of the sample table. However, this structure has a drawback in that when the voice coil motor moves with high speed, the magnet piece is separated from the steel ball due to the inertia of the sample table. This imposes a limitation upon the driving velocity as well as upon the stroke (driving velocity: 10 Hz, stroke: 5 mm or so). In addition, the carriage is attached onto the bobbin of the voice coil motor with the result that the weight being driven by the voice coil motor increases. In consequence, in the case of an apparatus requiring a high responsiveness, it is necessary to employ a voice coil motor whose output has an increased level in accordance with the increased inertia of the apparatus.
The increase in speed and stroke of the slide table has in recent years been demanded. This has required improvement of the slide table. To satisfy this requirement, it is important to make the slide table light in weight. The above-mentioned prior construction, however, is complicated in structure and therefore is difficult to miniaturize. Besides, since the sample table is in the form of a plate, i.e., small in thickness, difficulty is encountered in making the transversal stiffness of the air bearings large and there also exists a drawback that the manufacturing cost is high. Further, in case an acoustic lens is mounted on the sample table, a sample which is located beneath the sample table is difficult to observe because of being hindered by the sample table. This raises problem concerning the operating efficiency.